4 THE CLASSES OF PLANTS. 



reproduced in the circumference of the trunk, whence their name of 



EXOGENS. 



Among Exogens there are, however, two totally different modes in which 

 the influence of the pollen is communicated to the seed. The larger part 

 of this great class consists of plants provided with the apparatus called style 

 and stigma, through which pollen-tubes are introduced into the ovary 

 "during the act of fertilisation. But others are so constructed that the 

 pollen falls immediately upon the ovules, without the introduction of any 

 intermediate apparatus ; a peculiarity analogous to what occurs among 

 reptiles in the Animal Kingdom : and, as was to have been anticipated, the 

 plants in which this singular habit occm's prove, upon being collected 

 together, to form a group having no direct affinity with those among which 

 they had been previously associated. Hence Exogens have been broken up 

 into 1. Exogens proper, or those having an ovary, style, and stigma ; and 

 2. Gymxogexs, Avhich have neither. 



Among Endogens no difference has been remarked in the mode of propa- 

 gation, but a material peculiarity has been noticed in the manner of growth. 

 In the great mass of the class the stem and root are formed in a similar 

 way, or there is no considerable difference between them, and the leaves 

 have no articulation with the stem ; but in a part of them the root is 

 exactly like that of an Exogen without concentric circles, and the leaves 

 fall off the stem by a clean fracture, just as in that class. Such funda- 

 mental distinctions have given rise to the separation by me of Endogens 

 into 1. Endogens proper, and 2. Dictyogens. 



This gives us for the whole Vegetable Kingdom the following 



CLASSES. 

 Asexual, or Flowerless Plants. 

 Stems and leaves undistinguishable . . . I. THALLOGENS. 



Stems and leaves distinguishable . . . II. ACROGENS. 



Sexual, or Flowering Plants. 



Fructification springing from a thallus . . |||. RHIZOGENS. 



Fructification springing from a stem. 



Wood of stem arranged in a confused manner, youngest in the centre ; 



cotyledon single. 

 Leaves parallel-veined, permanent ; Root much 



Hke the stem internally . . IV.ENDOGENS. 



Leaves net-veined, deciduous ; Root with the 



wood in a solid concentric circle . . V. DICTYOGENS. 



Wood of stem arranged in a concentric or uniform manner, youngest at 



the circumference ; cotyledons 2 or more. 

 Seeds quite naked .... VI. GYMNOGENS. 

 Seeds enclosed in seed-vessels . . VII. EXOGENS. 



